The present invention relates generally to an improved trailer brake system for an expanded vehicle train including a tractor and multiple trailers, such as, for example, semitrailers or drawbar trailers, coupled in series thereto.
A brake system of the general type under consideration is described in EP 1188634 A2. In the conventional brake system described in EP 1188634 A2, an electronic control device is provided that is capable of, among other things, preventing wheel lock or apportioning braking force as a function of axle load.
Also, the electronic control device can generate an automatic brake signal, even without brake actuation by the vehicle train operator, to brake individual vehicle wheels or all wheels to effect handling stability control or prevent rollover of the vehicle train about its longitudinal axis.
Furthermore, for braking an additional trailer coupled to the first or preceding trailer to form an expanded vehicle train, brake pressure generated on the basis of brake actuation by the vehicle operator is typically relayed via the first trailer to the brake system of the attached additional trailer.
If, however, the first trailer is equipped with a brake system having a conventional electronic control device of the type described above, an automatic brake signal from the electronic control device has no braking effect on the additional trailer. Consequently, the electronic control function corresponding to the automatic brake signal, an example being a vehicle rollover prevention function, cannot be completely effective. Also, with the automatic braking of the first trailer, the handling stability behavior of the vehicle train can change in an undesired way if the additional trailer pushes on the first or preceding trailer.